| 引用本文: | 潘昭烨，张玉柱，黄春长，庞奖励，查小春，周亚利，朱艳，
贾雅娜，王浩宇，陈豆，肖奇立，王春梅.2022.汉江上游罗家滩剖面晚更新世以来沉积物粒度端元分析[J].地球环境学报,13(6):702-713 |
| PAN Zhaoye, ZHANG Yuzhu, HUANG Chunchang, PANG Jiangli, ZHA Xiaochun, ZHOU Yali,
ZHU Yan, JIA Yana, WANG Haoyu, CHEN Dou, XIAO Qili, WANG Chunmei.2022.Grain size end member analysis of the Late Pleistocene and Holocene sediments in the Luojiatan profile on the upper Hanjiang River[J].Journal of Earth Environment,13(6):702-713 |
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| 摘要: |
| 通过对汉江上游旬阳段开展野外考察，在罗家滩（LJT）发现夹有古洪水滞流沉积层（slackwater deposits，SWD）的风成黄土-古土壤剖面。对采集的沉积学样品进行粒度分析，利用Gen.Weibull函数分布的参数化端元模型反演得出4个端元，结合吸湿水等环境替代指标分析，探讨了各个端元所指示的不同沉积动力环境和物质来源。结果表明：在黄土层和土壤层中，EM1代表的主要是沉积物沉积后在亚洲夏季风影响下，经历强烈风化成壤作用形成的次生黏土矿物组分；EM2代表高空西风和东亚冬季风翻越秦岭而搬运的远源细粉砂组分；EM3代表山谷风从河谷中分布的河流沉积物和坡积碎屑物中以低空短距离形式搬运而来的粉尘物质，并且受到后期气候变化控制下的淋溶作用影响；EM4则代表山谷风从近源的河流沉积物和坡积碎屑物中搬运而来的粗颗粒物质。在古洪水SWD层中，EM1、EM2和EM3主要来源于汉江上游暴雨洪水侵蚀搬运的河谷两岸分布的表层沉积物；而EM4则明确代表河流特大/大洪水环境下搬运沉积的粗颗粒悬移质泥沙。该成果能够为区域环境变化研究提供指导和借鉴。 |
| 关键词: 环境变化 端元分析 粒度 风成黄土 汉江上游 |
| DOI：10.7515/JEE222031 |
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| 基金项目:国家自然科学基金项目（42277449，41977062，41971116）；黄土与第四纪地质国家重点实验室开放基金（SKLLQG2107） |
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| Grain size end member analysis of the Late Pleistocene and Holocene sediments in the Luojiatan profile on the upper Hanjiang River |
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PAN Zhaoye, ZHANG Yuzhu, HUANG Chunchang, PANG Jiangli, ZHA Xiaochun, ZHOU Yali,
ZHU Yan, JIA Yana, WANG Haoyu, CHEN Dou, XIAO Qili, WANG Chunmei
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1. College of Urban and Environmental Sciences, Northwest University, Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity, Xi’an 710127, China
2. School of Geography and Tourism, Shaanxi Normal University, Xi’an 710119, China
3. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
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| Abstract: |
| Background, aim, and scope Determining the material source of the aeolian loess-paleosol succession on the upper reaches of Hanjiang River can not only reveal rich information on the evolution of the Asian monsoon climate, but also help to understand the responses of extreme climatic and hydrological events in the basin to global climate change. The end member (EM) model can be used to identify sensitive grain size components of different material sources and sedimentary dynamic processes from sediments, and further reveal changes of the regional sedimentary environment. In this study, the parametric method was used to decompose the end member model of the Luojiatan (LJT) profile in the Xunyang section of the upper Hanjiang River. Based on these results combined with comprehensive analysis of environmental substitution indexes, such as hygroscopic water and geochemical elements, the different depository dynamic environments and material sources indicated by each end member were identified, and the sedimentological records of major flood events in the section were accurately identified. Materials and methods A total of 198 samples were collected from the LJT profile for grain size testing. After pretreatment, the grain size distributions were measured by a LS13320 laser particle size analyzer produced by Beckman Coulter, USA, with a detection range of 0.4—2000 μm. The results were analyzed by the AnalySize program based on MATLAB software, provided by Paterson and Heslop (2015). We calculated the chemical index of alteration (CIA), leaching coefficient, Rb/Sr ratio, and hygroscopic water of the above samples to assist in the determination of the source components. Results The grain size composition of the LJT profile could be decomposed into four main end members using the parametric method. The modal grain sizes of the four end members in the LJT profile were EM1=3.81 μm, EM2=8.60 μm, EM3=27.16 μm, and EM4=103.87 μm. Discussion According to the Sheppard triangle classification diagram, the loess samples from the LJT profile of the Xunyang section were mainly composed of silt, among which SWD2 was sandy silt, and the overall distribution was concentrated. The content of EM1 in the soil layer was significantly higher than those in all loess layers, and its variation trend was similar to those of the Rb/Sr ratio, the CIA, and hygroscopic water. The content of EM2 in the soil layer was significantly lower than those in all loess layers. The variation trend of EM3 was similar to that of the leaching coefficient. The contents of EM4 in all loess and soil layers were low, and there was no significant regularity. The contents of the EM1, EM2, and EM3 end members in the SWD layer of each paleoflood were similar to those in aeolian loess layers. The EM4 content of SWD2 was significantly higher than that in aeolian loess. Conclusions The results show that in each loess layer and soil layer, EM1 mainly represented the secondary clay mineral components formed by strong pedogenesis under the influence of the Asian summer monsoon after sediment deposition. EM2 represented the distant source of fine silt components transported by high-altitude westerly winds and the East Asian winter monsoon over the Qinling Mountains. EM3 represented dust transported by mountain and valley winds from the river sediments and slope deposits distributed across the river valley at low altitudes and over short distances, and was affected by eluviation under the control of later climate change. EM4 represented the coarse-grained material transported by mountain and valley winds from nearby river sediments and slope deposits. In each paleoflood SWD layer, the contents of EM1, EM2, and EM3 all were high and similar to each loess layer and soil layer, indicating that they were mainly derived from the surface soil sediments distributed across both sides with the river valley, eroded and transported by heavy rain and floods of the upper Hanjiang River. In addition, EM4 clearly represented coarse-grained suspended sediment transported and deposited by the river under extreme/large flood conditions. Recommendations and perspectives End member analysis of sediment grain sizes showed that this model was effective for identifying the sedimentary dynamic environment and material source of aeolian loess-paleosol and paleoflood SWDs, and can provide guidance and reference for the study of regional environment changes. |
| Key words: environmental change end member analysis grain size aeolian loess Hanjiang River |
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